a. Field of the invention:
The present invention is concerned with a breakaway mirror mounting for detachably attaching a rear view mirror device to the interior structure of a motor vehicle.
B. Description of the prior art:
A known rear view mirror device to be attached in breakaway fashion comprises a mirror supporting arm member and a base member secured to the body of a motor vehicle. One or more projections are provided on that surface of one of the two members which is to abut on the surface of the other member on which one or more accomodation holes for the projections are formed. The known rear view mirror device is detachably attached to the body of a motor vehicle via the base member by engaging the projections and accomodation holes with each other.
One of such known rear view mirror devices has been proposed in U.S. Pat. No. 3,703,270 to Tomlin et al. In Tomlin, an arm of the mirror is attached to a bracket by means of a ball-shaped joint which permits it to pivot and is held in place by a ring or socket cavity. The breakaway force of this construction can be adjusted by modifying the grade of the resilient plastics material of which the construction is made, the position of an annular recess surrounding the ring for holding the ball-shaped joint and the number and position of radial webs provided on the peripheral wall of the ring. The difficulty with this type of device is that the molding of members constituting the device is rather difficult and that it is therefore difficult to arrange the structure such that the amount of force which causes the mirror to break away can be easily determined in advance. As a result, it is difficult to make sure that that force will be uniform for each such apparatus produced. This is particularly important since detachment of the mirror, except under emergency conditions, can be very dangerous and at the very least might be inconvenient. On the other hand, failure of the mirror to properly detach could have disastrous conditions. Accordingly, it is extremely important to be able to determine easily and accurately the amount of force required for breakaway.